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--- en:multiasm:piot:chapter_4_3 [2025/05/31 09:20] – marcin
+++ en:multiasm:piot:chapter_4_3 [2026/01/19 15:08] (current) – marcin
@@ Line 6: / Line 6: @@
 **R0-R15:**
-Basic general-purpose registers used for various arithmetic and logical operations.
+Basic general-purpose registers are used for various arithmetic and logical operations.
 **R16-R31:**
 General-purpose registers that can be used with immediate
-{{:en:multiasm:piot:avr_general_purpose_register.png?400|}}
+Comparison Table: AVR Registers R0–R15 vs. R16–R31
+^  Feature                     ^  R0–R15                                                            ^  R16–R31                                        ^
+|  Instruction compatibility   |  Cannot be used with immediate instructions (LDI, CPI, ORI, ANDI)  |  Fully compatible with immediate instructions   |
+|  Opcode encoding             |  Not encodable in 4‑bit register fields                            |  Encodable in all immediate‑type formats        |
+|  Typical compiler usage      |  Less preferred; used for temporary or special roles               |  Preferred for arithmetic and logic operations  |
+|  Special-purpose roles       |  R0: scratch<br>R1: constant zero                                  |  R26–R31 used as X/Y/Z pointer registers        |
+|  Pointer support             |  No                                                                |  Yes: X, Y, Z pointers                          |
+|  Efficiency                  |  Less efficient for immediate operations                           |  More efficient due to shorter opcodes          |
+|  Multiplication involvement  |  R0/R1 used implicitly for results                                 |  Not used by multipliers                        |
+|  Suitability in ASM          |  Limited; avoid with immediates; R0/R1 have special rules          |  Recommended for general ALU operations         |
+|  GCC policy                  |  R1 must remain 0; R0 is volatile                                  |  Treated as normal general-purpose registers    |
+<figure avr_registers>
+{{en:multiasm:piot:avr_register1.svg?300|AVR Registers}}
+<caption>AVR Registers</caption>
+</figure>
 **The X-register, Y-register, and Z-register:**
 address pointers for indirect addressing
-R26-R31: These registers have additional functions as 16-bit address pointers for indirectly addressing the data space. They are defined as X, Y, and Z registers.
+R26-R31: These registers serve as 16-bit address pointers for indirect addressing of the data space. They are defined as X, Y, and Z registers.
+<figure avr_registers>
+{{en:multiasm:piot:x_y_z_registers.svg?400|Extended registers}}
+<caption>Etended Registers</caption>
+</figure>
 **Other registers:**
@@ Line 25: / Line 45: @@
 EIND: Register concatenated with the Z-register, enabling indirect jump and call to the entire program space on MCUs with more than 64K words (128 KB) of program space.
+<table Register properties>
+<caption>Register properties</caption>
+^  Register  ^  Purpose                              ^  Combined With  ^  Enables                                           ^
+|  RAMPX     |  Extends data addressing              |  X register     |  Access to data above 64 KB using X                |
+|  RAMPY     |  Extends data addressing              |  Y register     |  Access to data above 64 KB using Y                |
+|  RAMPZ     |  Extends data and program addressing  |  Z register     |  Access to data and constants above 64 KB using Z  |
+|  RAMPD     |  Extends data addressing              |  Z register     |  Direct access to data above 64 KB                 |
+|  EIND      |  Extends program addressing           |  Z register     |  Jumps and calls to program memory above 128 KB    |
+</table>
+All of the registers RAMPX, RAMPY, RAMPZ, RAMPD, and EIND are located in the extended I/O space of AVR microcontrollers. This area typically occupies addresses 0x3B–0x3F, although the exact address of each register depends on the specific AVR device. The precise locations can always be found in the Register Summary section of the device datasheet.

en/multiasm/piot/chapter_4_3.1748672429.txt.gz · Last modified: 2025/05/31 09:20 by marcin